C-P: ArmPlatformPkg: Add Readme file

Added a readme file that explains the software framework for dynamic
generation of HEST table.

Signed-off-by: Omkar Anand Kulkarni <omkar.kulkarni@arm.com>
Change-Id: Iafe54949948ddf15c1d769cf5886caba589409ba
(cherry picked from commit 9486a4a10844142e872ed6553aac420a1f66a9bf)

ArmPlatformPkg/Drivers/HestMmErrorSources/Readme.md

@@ -0,0 +1,70 @@
+# HEST & SDEI
+
+Hardware Error Source Table HEST [1] and Software Delegated Exception Interface
+SDEI [2] ACPI tables are used to accomplish firmware first error handling.This
+patch series introduces a framework to build and install the HEST ACPI table
+dynamically.
+
+The following figure illustrates the possible usage of the dynamic
+generation of HEST ACPI table.
+
+``` ascii art
+                                    NS | S
++--------------------------------------+--------------------------------------+
+|                                      |                                      |
+|+-------------------------------------+---------------------+                |
+||               +---------------------+--------------------+|                |
+||               |                     |                    ||                |
+|| +-----------+ |+------------------+ | +-----------------+|| +-------------+|
+|| |HestTable  | ||  HestErrorSource | | | HestErrorSource ||| | DMC-620     ||
+|| |  DXE      | ||        DXE       | | |  StandaloneMM   ||| |Standalone MM||
+|| +-----------+ |+------------------+ | +-----------------+|| +-------------+|
+||               |GHESv2               |                    ||                |
+||               +---------------------+--------------------+|                |
+||          +--------------------+     |                     |                |
+||          |PlatformErrorHandler|     |                     |                |
+||          |        DXE         |     |                     |                |
+||          +--------------------+     |                     |                |
+||FF FWK                               |                     |                |
+|+-------------------------------------+---------------------+                |
+|                                      |                                      |
++--------------------------------------+--------------------------------------+
+                                       |
+                   Figure: Dynamic Hest Table Generation.
+```
+
+All the hardware error sources are added to HEST table as GHESv2[3] error source
+descriptors. The framework comprises of following DXE and MM drivers:
+
+- HestTableDxe:
+  Builds HEST table header and allows appending error source descriptors to the
+  HEST table. Also provides protocol interface to install the built HEST table.
+
+- HestErrorSourceDxe & HestErrorSourceStandaloneMM:
+  These two drivers together retrieve all possible error source descriptors of
+  type GHESv2 from the MM drivers implementing HEST Error Source Descriptor
+  protocol. Once all the descriptors are collected HestErrorSourceDxe appends
+  it to HEST table using HestTableDxe driver.
+
+- PlatformErrorHandlerDxe:
+  Builds and installs SDEI ACPI table. This driver does not initialize(load)
+  until HestErrorSourceDxe driver has finished appending all possible GHESv2
+  error source descriptors to the HEST table. Once that is complete using the
+  HestTableDxe driver it installs the HEST table.
+
+This patch series provides reference implementation for DMC-620 Dynamic Memory
+Controller[4] that has RAS feature enabled. This is platform code
+implemented as Standalone MM driver in edk2-platforms.
+
+## References
+
+[1]: ACPI 6.3, Table 18-382, Hardware Error Source Table
+[2] : SDEI Platform Design Document, revision b, 10 Appendix C, ACPI table definitions for SDEI
+[3] : ACPI Reference Specification 6.3, Table 18-393 GHESv2 Structure
+[4] : DMC620 Dynamic Memory Controller, revision r1p0
+[5] : UEFI Reference Specification 2.8, Appendix N - Common Platform Error
+      Record
+[6] : UEFI Reference Specification 2.8, Section N.2.5 Memory Error Section
+
+Link to github branch with the patches in this series -
+<https://github.com/omkkul01/edk2/tree/ras_firmware_first_edk2>